The overall objective of the proposed research is to elucidate in molecular terms the mechanisms by which purified natural and cloned human leukocyte (IFN-Alpha) and immune (IFN-Gamma) interferons act to affect a wide variety of fundamental viral and cellular processes. The specific aims are as follows: (1) To elucidate the molecular basis of the differential antiviral effects of human IFN-Alpha and IFN-Gamma on the replication of reovirus as compared to vesicular stomatitis virus in human amnion and human fibroblast cells. Natural and cloned IFN-Alpha subspecies inhibit VSV but not reovirus replication in human amnion and fibroblast cells; however, cloned IFN-Gamma inhibits both VSV and reovirus in the human cells. The antiviral actions of IFN-Alpha and IFN-Gamma are synergistic for VSV, but not for reovirus. (2) To construct recombinant DNAs between the dsDNA copies of reovirus S1 and S4 genes and simian virus 40, and to study the effect of IFN on the expression of SV40-reovirus(S1,S4) recombinant DNAs in transfected monkey cells as an approach to elucidating the molecular basis of the sensitivity of reovirus mRNA translation to IFN and the resistance of SV40 mRNA translation to IFN. To construct additional SV40-VSV(G protein) recombinant DNAs, and to study the effect of IFN on their expression as compared to that of SV40-reovirus (S1,S4) recombinants. The translation of SV40 mRNA is not inhibited but the translation of reovirus mRNA is inhibited in IFN-treated monkey cells doubly infected with SV40 and reovirus; the translation of SV40 early RNA is also not inhibited in IFN-treated SV3T3 cells although the replication of both reovirus and VSV are inhibited. The synthesis of VSV G protein in COS cells transfected with an SV40-VSV(G) expression vector is inhibited by IFN. (3) To continue our efforts to determine the biochemical basis, both in vitro and in vivo, of the difference in translational efficiency of the s-class mRNAs of reovirus. The rate of synthesis of polypeptides Sigma1 and Sigma3 differs by more than 10-fold under conditions where the molar amount of their mRNAs differ by less than 2-fold. The health relatedness of the proposed research stems from the likelihood that the work may contribute to a better understanding of regulatory mechanisms possibly operative in normal cells as well as virus-infected cells, and that the elucidation of the molecular mechanisms of action of the different types of interferons is of immediate importance in view of the potential applications of IFN in the clinic.